Don't worry about me, I know what I'm doing. But the bulge in the intake works for one reason: it creates a vacuum, which is why I used them as an example. They may not have dynoed the intake and checked the liquid dynamics in effect, but even a moderately designed bulge will create power.
Using a principle almost like Hemoltz Resonance, the bulge creates a low pressure zone in comparison to the rest of the intake piping causing a vacuum to form in the bulge. The engine working as the pump keeps sucking in the extra air and the vacuum keeps building until the volume of air in the entire system averages out at a higher mass than with a linear-diametre piping system.
The reason why the J's Racing unit that the Password:JDM one is based off of looks the way it does is because of the need to smooth the air out over the routing of the piping, which is in the form of an 's'. Mind you, smoothing out the bulge in a straight pipe would also yield benefits.
Mind you, this is from my non-expertise liquid dynamics understanding. I've only been studying this stuff by myself for about 2-3 years, so I am nowhere near schooled. There may be other principles involved. that I am not aware of that change the theory slightly, but I research every chance I get so I can innovate or improve on my current understanding of physics, chemistry and so on.